The objectives of this trial are 1) to determine the response rate and duration of response to 9-aminocamptothecin in patients with metastatic breast cancer, progressive after one prior chemotherapy regimen, 2) to describe toxicity associated with the regimen, 3) to determine 9- aminocamptothecin pharmacokinetic parameters. During the past year, 4 additional patients were enrolled in this trial. No serious adverse events occurred. This trial will continue to accrue patients.